1. Technical Field
The present invention relates to the technical field of liquid crystal devices. In particular, the present invention relates to a structure of a liquid crystal device which can change a display mode between a reflective mode and a transmissive mode, and to an electronic device using the liquid crystal device.
2. Background Art
Reflective liquid crystal devices consuming small amounts of electrical power have been widely used in portable devices and display sections in various apparatuses. Since, however, the display is performed by external light, an image is not visible in dark environments. Thus, some proposed liquid crystal devices use external light in a lighted environment as in general reflective liquid crystal devices, and an internal light source in dark environments so as to maintain a visible state. As disclosed in Japanese Patent Application Laid-Open Nos. 57-049271, 57-049271, and 57-049271, each device has a polarizer, a transflector, and a backlight, in that order, at the outer face, away from the viewer, in a liquid crystal panel. The liquid crystal device performs reflective display using external light reflected by the transflector in a lighted environment, and transmissive display using light from the backlight, which is turned on so as to maintain a visible state, transmitted through the transflector in dark environments.
Another liquid crystal device having improved brightness in a reflective display mode is disclosed in Japanese Patent Application Laid-Open No. 8-292413. The liquid crystal device has a transflector, a polarizer, and a backlight, in that order, at the outer face, away from the viewer, of the liquid crystal panel. The device performs reflective display using external light reflected by the transflector when the environment is light, and transmissive display using light from the backlight, which is turned on so as to maintain a visible state, transmitted through the polarizer and the transflector. Since the polarizer is not provided between the liquid crystal cell and the transflector, brighter display is achieved in a reflective mode compared to the above-mentioned liquid crystal devices.
In the liquid crystal device disclosed in Japanese Patent Application Laid-Open No. 8-292413, however, a transparent substrate is disposed between a liquid crystal layer and the transflector; hence, problems, such as double imaging and blurred imaging, occur.
Color liquid crystal display has been required with recent development of portable devices and office automation devices. Apparatuses using reflective liquid crystal devices also require color display. In a combination of the liquid crystal device disclosed in the above patent application with a color filter, the transflector is arranged behind the liquid crystal panel. Thus, the thick transparent substrate lies between the liquid crystal layer with the color filter and the transflector, resulting in occurrence of double imaging or blurred imaging due to parallax and insufficient coloring.
In order to solve the problems, Japanese Patent Application Laid-Open No. 9-258219 discloses a reflective color liquid crystal device in which a reflector is disposed so as to come into contact with the liquid crystal layer. This liquid crystal device, however, cannot display visible images in dark environments.
In addition, Japanese Patent Application Laid-Open No. 7-318929 discloses a transflective liquid crystal device in which a pixel electrode functioning as a transflective film is provided on the inner face of the liquid crystal cell. Since this liquid crystal device has a transflective film such as a metallic thin film having fine defects including pinholes, dimples, and fine openings, an oblique electric field which is generated on the periphery of the defects and openings causes unsatisfactory orientation of the liquid crystal, producing many technical problems which inhibit high-quality image display. That is, a high contrast and brightness are not achieved, and coloring due to wavelength dispersion of light inevitably occurs both in a reflective display mode and a transmissive display mode. Furthermore, it is difficult to achieve both prevention of brightness defects at the gap between pixel electrodes or an improvement in contrast and an improvement in brightness in a reflective display mode. Furthermore, the production process requires addition of a particular step; hence, the device satisfies with great difficulty a typical demand for reduction in production cost in this technical field.
The present invention has been accomplished in view of the above-mentioned problems and has an object to provide a transflective liquid crystal device, which is changeably used both in a reflective display mode and a transmissive display mode, does not produce double imaging and blurred imaging due to parallax, can display high-quality images, and to provide an electronic apparatus using the liquid crystal device.
The object of the present invention is achieved by a first liquid crystal device including a pair of first and second transparent substrates; a liquid crystal layer disposed between the first and second substrates; a transparent electrode formed on a face of the first substrate on the side of the liquid crystal layer; a reflective electrode formed on a face of the second substrate and having an oblong slit, the face contacting the liquid crystal layer; and an illumination unit provided on another face of the second substrate on the opposite side of the liquid crystal layer.
In accordance with the first liquid crystal device of the present invention, the reflective electrode reflects external light incident on the first substrate towards the liquid crystal layer in a reflective display mode. Since the reflective electrode is provided on the liquid crystal layer face of the second substrate, no gap is substantially formed between the liquid crystal layer and the reflective electrode and thus double imaging and blurred imaging due to parallax do not occur. In a transmissive display mode, illuminated light incident on the second substrate from the illumination unit enters the liquid crystal layer through the slits. Thus, the illuminated light enables bright display in dark environments.
Since the reflective electrode has oblong slits, an oblique electric field (hereinafter referred to as an xe2x80x9coblique electric field due to the short sides of the slitxe2x80x9d) is applied to the liquid crystal layer between the edges of each reflective electrode defining short sides of a slit and opposingly disposed at a relatively large distance (edges of each reflective electrode opposing each other at each end of two long sides of a slit) and the transparent electrode. An oblique electric field (hereinafter referred to as an xe2x80x9coblique electric field due to the long sides of the slitxe2x80x9d) is simultaneously applied to the liquid crystal layer between edges of each reflective electrode defining long sides of a slit and opposingly disposed at a relatively short distance (edges of each reflective electrode opposing each other at each end of two short sides of a slit) and the transparent electrode. The components of the oblique electric field due to the short sides of the slit and the same of the oblique electric field due to the long sides of the slit are perpendicular to each other in the substrate plane. When these two oblique electric fields interact with liquid crystal molecules in the vicinity of the slit, the intensities of these two oblique electric fields determine the direction of movement of liquid crystal molecules. If the slit is a square, these two oblique electric fields are equivalent to each other. Thus, the relationship between these intensities is reversed at some positions. As a result, the directions of movement of liquid crystal molecules are different at these positions, and insufficient alignment of the liquid crystal appears as a relatively large domain. That is, display defects occur in the domain. Insufficient alignment is most noticeable when these two oblique electric fields have the same intensity. If one is higher than the other in a region, movement of liquid crystal molecules in the region is controlled by the oblique electric field having a higher intensity and thus becomes uniform. In the present invention, the oblique electric field (the in-substrate-plane component is parallel to the longitudinal direction of the slit) due to the short sides of the slit is reduced in response to the length of long sides of the slit. In contrast, the oblique electric field (the in-substrate-plane component is perpendicular to the longitudinal direction of the slit) due to the long sides of a slit is relatively increased in response to the length of the short sides of the slit. In the present invention, therefore, the oblique electric field due to the long sides of the slit controls the movement of liquid crystal molecules. Accordingly, insufficient alignment is reduced in the vicinity of the slit and display defects are reduced. Furthermore, electrical power consumed by the liquid crystal device can be reduced by a reduced threshold voltage, since the liquid crystal is partly driven using the oblique electric field due to the long sides of the slit.
When a countermeasure is taken only for the oblique electric field due to the long side of the slit, and no consideration is given to the oblique electric field due to the short side of the slit, overall insufficient alignment of the liquid crystal caused by the oblique electric field can be reduced. Alternatively, voluntary use of the oblique electric field (for example, setting of various operational parameters for reducing adverse effects of insufficient alignment of the liquid crystal caused by the oblique electric field in practice or for satisfactorily driving of the liquid crystal by the oblique electric field, setting of specifications of constituents and parts, and device design) facilitates satisfactory driving of the liquid crystal. If the slit is square, countermeasures must be taken for two oblique electric fields, resulting in very difficult design and production of the liquid crystal device. Furthermore, voluntary use of these two oblique electric fields is almost impossible in practice.
As materials for the reflective electrode, metals containing aluminum as a primary component are used. Metals which can reflect external visible light, such as chromium and silver, can also be used without limitation. Since the reflective electrode has a function of reflecting external light and a function of applying a voltage to the liquid crystal, this device structure has advantages in production and design and facilitates cost reduction compared to a structure having independently formed reflective electrodes and pixel electrodes.
Oblong slits can be readily formed by a photostep using a resist, a development step, and then a peeling step. It means that there is no need to increase the number of production processes since the slits can be simultaneously formed when the reflective electrodes are formed. The width of each slit is in a range of preferably 0.01 xcexcm to 20 xcexcm, and is more preferably 1 xcexcm to 5 xcexcm. Thus, a reflective display mode and a transmissive display mode can be simultaneously achieved without deterioration of image quality due to provision of the slit, since a viewer cannot recognize such a structure. Preferably, the slit has an area ratio of 5% to 30% with respect to the reflective electrode. Such a ratio can moderate decreased brightness in a reflective display mode, and achieves a transmissive display mode by light incident on the liquid crystal layer via the slits of the reflective electrodes.
The first liquid crystal device can be driven by various conventional driving system, such as a passive matrix driving system, a thin film transistor (TFT) active matrix driving system, a thin film diode (TFD) active matrix driving system, or a segment driving system.
In an embodiment of the first liquid crystal device in accordance with the present invention, the reflective electrode comprises a plurality of stripe electrodes at a predetermined gap and the slit extends in the longitudinal direction of the reflective electrode.
According to this embodiment, a countermeasure for the oblique electric field caused by the long sides of the slit is effective for the oblique electric field caused by gaps between the reflective electrodes. Furthermore, the reflective electrodes and the slits can be simultaneously formed, and the design of the mask used in the formation can be simplified. Thus, this embodiment has advantages in a structure, production, and design of the device.
In this embodiment in which the stripe reflective electrodes are formed in stripe, the transparent electrode may comprise a plurality of stripe electrodes at a predetermined gap in the direction perpendicular to the reflective electrode and the slit may extend to a position facing the gap between the transparent electrodes.
In such a structure, edges of each reflective electrode defining short sides of each slit and opposingly disposed at a relatively large distance lie in a position in which the transparent electrode is not formed. That is, the edges lie distant from a portion of the reflective electrode in which a voltage is applied between the transparent electrode and the reflective electrode. Thus, the effect of the oblique electric field due to the short side of the slit can be significantly reduced.
In this embodiment in which the reflective electrodes are formed in stripe, the slit may extend over a plurality of pixels.
In such a structure, each pixel does not have edges of reflective electrodes defining short sides of slits opposingly disposed at a relatively large distance; hence, the effect of the oblique electric field which is applied to the liquid crystal layer between the edges of the reflective electrode and the transparent electrode due to the short side (a shorter side is preferable) of the slit can be significantly reduced.
In this case, the slit may extend to the exterior of the image display region.
In such a structure, each pixel does not have edges of reflective electrodes defining short sides of slits opposingly disposed at a relatively large distance; hence, the effect of the oblique electric field due to the short side (a shorter side is preferable) of the slit can be almost completely reduced.
In this embodiment in which electrodes are formed in stripe, the width of a slit may be substantially equal to a gap between reflective electrodes.
In such a structure, a countermeasure for or voluntary use of, the oblique electric field due to the long side of the slit is also effective as a countermeasure for or voluntary use of, the oblique electric field due to the gap between the reflective electrodes. Furthermore, the slits can be simultaneously formed when the reflective electrodes are formed and design of the photomask is simplified; hence this structure has significant advantages in production and design of the device. Herein xe2x80x9csubstantially equalxe2x80x9d means that the width of a slit is almost equal to the gap between the reflective electrodes so that the effect of the oblique electric field due to the long side of the slit and the effect of the oblique electric field caused by the gap between the reflective electrodes appear equally, or almost equal enough that they can be formed utilizing photomasks having the same width.
In another embodiment of the first liquid crystal device in accordance with the present invention, the width of the slit is 4 xcexcm or less.
As a result of experiments and research by the present inventors, the variation of the threshold voltage of the liquid crystal with the width of the slit was elucidated. Specifically, when the slit width is larger than 4 xcexcm, the threshold voltage of the liquid crystal significantly differs between the reflective display mode and the transmissive display mode; hence, it is difficult or impossible to set a driving voltage enabling a satisfactory contrast and a variation of density in both display modes. When the width of the slit is larger than 4 xcexcm, a high intensity electric field would likely be necessary to drive the liquid crystal facing the slit. Since the width of the slit is 4 xcexcm or less in this embodiment, the threshold voltage of the liquid crystal can be set to be substantially the same in both the reflective display mode and the transmissive display mode. For example, when the width of the slit is 2 xcexcm and the width of the reflective electrode is 10 xcexcm, a driving voltage facilitating a high contrast and a large change in density can be readily set.
In another embodiment of the first liquid crystal device in accordance with the present invention, an angle "xgr" between the alignment direction of the liquid crystal molecule substantially in the center between the transparent electrode and the reflective electrode and the longitudinal direction of the slit is in a range of xe2x88x9260xc2x0xe2x89xa6"xgr"xe2x89xa660xc2x0.
According to this embodiment, the angle between the alignment direction of liquid crystal molecules, which lie substantially in the center between the transparent electrode and the reflective electrode and have the highest mobility, and the longitudinal direction of the slit shifts by 30xc2x0 or more from a right angle. Thus, when a voltage is applied between the transparent electrode and the reflective electrode, the alignment state of the liquid crystal molecules changes satisfactorily with almost no formation of a tilt domain. Thus, the threshold voltage during driving of the liquid crystal can be reduced, resulting in reduced power consumption of the liquid crystal device. Furthermore, display defects, such as disclination due to the tilt domain in the liquid crystal layer, are avoidable. A significant tilt domain is generated if the angle "xgr" is outside the range of xe2x88x9260xc2x0xe2x89xa6"xgr"xe2x89xa660xc2x0, because the alignment direction of the liquid crystal molecules is perpendicular to the longitudinal direction of the slit. Thus, the driving voltage increases. The above advantage is particularly noticeable in a range of xe2x88x9230xc2x0xe2x89xa6"xgr"30xc2x0. The tilt domain is the same as the phenomenon described in xe2x80x9cLiquid Crystal Device Handbookxe2x80x9d, p. 254, edited by Committee 142 in Japan Society for the Promotion of Science, and published by The Daily Industrial News. The tilt domain in the present invention, however, is generated by the direction of the applied voltage, not by the pretilt angle.
In another embodiment of the first liquid crystal device of the present invention, an angle xcex4 between the alignment direction of a liquid crystal molecule in the vicinity of the reflective electrode and the longitudinal direction of the slit is in a range of xe2x88x9230xc2x0xe2x89xa6xcex4xe2x89xa630xc2x0.
According to this embodiment, the alignment direction of the liquid crystal molecule in the vicinity of the reflective electrode having a predetermined pretilt angle is nearly parallel to, rather than perpendicular to, the longitudinal direction of the slit. Thus, there is substantially no possibility of the liquid crystal molecule at the substrate interface being reverse-tilted by the effect of the oblique electric field. Display defects such as disclination due to the reverse tilt domain are, therefore, avoidable. Thus, the threshold voltage during driving of the liquid crystal can be reduced, resulting in reduced power consumption of the liquid crystal device. If the angle xcex4 is in a range outside xe2x88x9230xc2x0xe2x89xa6xcex4xe2x89xa630xc2x0, the liquid crystal molecule at the substrate interface is noticeably reverse-titled by the effect of the oblique electric field causing display defects. Furthermore, the driving voltage increases, resulting in increased power consumption. The above advantage is particularly noticeable in a range of xe2x88x9210xc2x0xe2x89xa6xcex4xe2x89xa610xc2x0.
In another embodiment of the first liquid crystal device in accordance with the present invention, the device is in a dim or black state when not driven.
Since the device is in a dim or black state when not driven in this embodiment, optical leakage from boundaries between non-driven liquid crystal pixels or dots can be reduced in a transmissive display mode, resulting in transmissive display having a high contrast. Furthermore, undesirable reflection at boundaries between pixels or dots can be reduced in a reflective display mode, resulting in a display having a high contrast.
In another embodiment of the first liquid crystal device in accordance with the present invention, a shading layer is formed on at least one of the face of the first substrate on the side of the liquid crystal layer and the face of the second substrate on the side of the liquid crystal layer, so as to at least partly cover the gap between the reflective electrodes.
According to this embodiment, optical leakage from boundaries between non-driven liquid crystal pixels or dots can be reduced in a transmissive display mode, resulting in transmissive display having a high contrast. Furthermore, undesirable reflection at boundaries between pixels or dots can be reduced in a reflective display mode, resulting in a display having a high contrast.
In another embodiment of the first liquid crystal device in accordance with the present invention, the device further includes a first polarizer provided on another face of the first substrate on the opposite side of the liquid crystal layer, and at least one first retardation film disposed between the first substrate and the first polarizer.
According to this embodiment, the first polarizer primarily achieves satisfactory display control in both the reflective and transmissive display modes, and the first retardation film primarily reduces effects on tonality, such as coloring, due to the wavelength dispersion of light.
In another embodiment of the first liquid crystal device in accordance with the present invention, the device further includes a second polarizer disposed between the second substrate and the illumination unit, and at least a second retardation film disposed between the second substrate and the second polarizer.
According to this embodiment, the second polarizer primarily achieves satisfactory display control in the transmissive display mode, and the second retardation film primarily reduces effects on tonality, such as coloring, due to the wavelength dispersion of light.
In another embodiment of the first liquid crystal device in accordance with the present invention, the reflective electrode contains 95% by weight or more of aluminum and has a thickness of 10 nm to 40 nm.
According to this embodiment, a thin transflective type reflective electrode is formed. According to experiments, the transflective reflective electrode has a transmittance of 1% to 40% and a reflectance 50% to 95% within the above thickness range.
In another embodiment of the first liquid crystal device in accordance with the present invention, the device further includes a color filter provided between the reflective electrode and the first substrate.
According to this embodiment, reflective color display by external light and transmissive color display using an illumination unit are available. Preferably, the color filter has a transmittance of 25% or more for light of any wavelength within a range of 380 nm to 780 nm. Bright reflective and transmissive color display is thereby achieved.
In another embodiment of the first liquid crystal device in accordance with the present invention, the device further includes a diffuser on another face of the first substrate on the opposite side of the liquid crystal layer.
According to this embodiment, the diffuser makes the mirror face of the reflective electrode look as a diffusing face (white surface). Diffusion by the diffuser enables display with a wide view angle. The diffuser may be disposed at any position above the face of the first substrate on the opposite side of the liquid crystal layer. Preferably, the diffuser is disposed between the polarizer and the first substrate in consideration of the effect of back scattering (scattering of the external light towards the incident side of it). The back scattering not contributing to the display of the liquid crystal device causes a decreased contrast in a reflective display mode. When the diffuser is disposed between the polarizer and the first substrate, the polarizer can reduce the quantity of light of back scattering to approximately one-half.
In another embodiment of the first liquid crystal device in accordance with the present invention, the reflective electrode has irregularities.
According to this embodiment, the irregularities eliminate the mirroring on the face of the reflective electrode and make the mirror face look as a diffusing face (white face). Diffusion by the irregularities enables display with a wide view angle. The irregularities may be formed by forming a photosensitive acrylic resin layer under the reflective electrode, or by roughening the underlying glass substrate with aqueous hydrogen fluoride. It is preferable in order to achieve satisfactory alignment of the liquid crystals that a transparent planarization film be formed on the irregular surface of the reflective electrode so that the surface contacting the liquid crystal layer (the surface on which an alignment film is formed) is planarized.
In another embodiment of the first liquid crystal device in accordance with the present invention, the reflective electrode is a composite of a reflective layer and a transparent electrode layer.
According to this embodiment, even if the reflective electrode with slits is not composed of a reflective and conductive single film, the reflective electrode can be obtained by making the reflective layer reflect external light, and the transparent electrode layer apply a driving voltage to the liquid crystal.
The above-mentioned object of the present invention is also achieved by a first electronic apparatus provided with the first liquid crystal device.
The first electronic apparatus in accordance with the present invention uses a transflective liquid crystal device or a color transflective liquid crystal device without double imaging and blurred imaging due to parallax, and can change a display mode between a reflective mode and a transmissive mode. Thus, the electronic apparatus can display high-quality images in any lighted or dark environment regardless of the level of ambient or external light.
The object of the present invention is also achieved by a second liquid crystal device including a pair of first and second transparent substrates; a liquid crystal layer disposed between the first and second substrates; a transparent electrode formed on a face of the liquid crystal layer side of the first substrate; a reflective electrode formed on a face of the liquid crystal layer side of the second substrate; an illumination unit provided on another face of the second substrate on the opposite side of the liquid crystal layer; a first polarizer provided on another side of the first substrate on the opposite side of the liquid crystal layer; at least one first retardation film disposed between the first substrate and the first polarizer; a second polarizer disposed between the second substrate and the illumination unit; and at least a second retardation film disposed between the second substrate and the second polarizer.
According to the second liquid crystal device of the present invention, the reflective electrode reflects external light incident on the first substrate towards the liquid crystal layer in a reflective display mode. Since the reflective electrode is provided on the face of the second substrate on the side of the liquid crystal layer, no gap is substantially formed between the liquid crystal layer and the reflective electrode. Thus, double imaging and blurred imaging due to parallax do not occur. On the other hand, the reflective electrode comprising a transflective layer transmits light which emerges from the illumination unit and is incident on the second substrate towards the liquid crystal layer in a transmissive display mode. Thus, light from the light source achieves bright display in a dark environment. The transflective layer may be a reflective film having oblong slits or square fine openings so that light partly passes through the film, as in the above-mentioned first liquid crystal of the present invention, a thin metal transflective film having fine defects, such as pinhole defects or dimples, or a film which shows overall transflective characteristics. Alternatively, the layer may be composed of a plurality of stripes or island reflective electrodes formed with a predetermined gap.
Since the second liquid crystal device has the first polarizer, the first retardation film, the second polarizer, and the second retardation film, the first and the second polarizers satisfactorily control display in both the reflective and transmissive display modes. The first retardation film reduces effects on tonality, such as coloring, due to the wavelength dispersion of light in a reflective display mode, whereas the second retardation film reduces effects on tonality, such as coloring, due to the wavelength dispersion of light in a transmissive display mode. The second liquid crystal device can be driven by various conventional driving system, such as a passive matrix driving system, a TFT active matrix driving system, a TFD active matrix driving system, or a segment driving system.
In an embodiment of the second liquid crystal device of the present invention, the device is in a dim or black state when not driven.
Since the device is in a dim or black state when not driven in this embodiment, optical leakage from boundaries between non-driven liquid crystal pixels or dots can be reduced in a transmissive display mode, resulting in transmissive display having a high contrast. Furthermore, undesirable reflection at boundaries between pixels or dots can be reduced in a reflective display mode, resulting in a display having a high contrast.
In another embodiment of the second liquid crystal device in accordance with the present invention, a shading layer is formed on at least one of the face of the first substrate on the side of the liquid crystal layer and the face of the second substrate on the side of the liquid crystal layer so as to at least partly cover the gap between the reflective electrodes.
According to this embodiment, optical leakage from boundaries between non-driven liquid crystal pixels or dots can be reduced in a transmissive display mode, resulting in transmissive display having a high contrast. Furthermore, undesirable reflection, which does not contribute to the display, at boundaries between pixels or dots can be reduced in a reflective display mode, resulting in a display having a high contrast.
In another embodiment of the second liquid crystal device in accordance with the present invention, the reflective electrode contains 95% by weight or more of aluminum and has a thickness of 10 nm to 40 nm.
According to this embodiment, a thin transflective type reflective electrode is formed. According to experiments, the transflective type reflective electrode has a transmittance of 1% to 40% and a reflectance 50% to 95% within the above thickness range.
In another embodiment of the second liquid crystal device in accordance with the present invention, the device further includes a color filter provided between the reflective electrode and the first substrate.
According to this embodiment, reflective color display by external light and transmissive color display using an illumination unit are available. Preferably, the color filter has a transmittance of 25% or more for light of any wavelength within a range of 380 nm to 780 nm. Bright reflective and transmissive color displays are thereby achieved.
In another embodiment of the second liquid crystal device in accordance with the present invention, the device further includes a diffuser on another face of the first substrate on the opposite side of the liquid crystal layer.
According to this embodiment, the diffuser makes the mirror face of the reflective electrode look as a diffusing face (white surface). Diffusion by the diffuser enables display with a wide view angle. The diffuser may be disposed at any position above the face of the first substrate on the opposite side of the Liquid crystal layer. Preferably, the diffuser is disposed between the polarizer and the first substrate in consideration of the effect of back scattering (scattering of the external light towards the incident side of it). The back scattering not contributing to the display of the liquid crystal device causes a decreased contrast in a reflective display mode. When the diffuser is disposed between the polarizer and the first substrate, the polarizer can reduce the quantity of light of back scattering to approximately one-half.
In another embodiment of the second liquid crystal device in accordance with the present invention, the reflective electrode has irregularities.
According to this embodiment, the irregularities eliminate the mirroring on the face of the reflective electrode and render the mirror face into a diffusing face (white face). Diffusion by the irregularities enables display with a wide view angle. The irregularities may be formed by forming a photosensitive acrylic resin layer under the reflective electrode, or by roughening the underlying glass substrate with aqueous hydrogen fluoride. It is preferable in order to achieve satisfactory alignment of the liquid crystals that a transparent planarization film be formed on the irregular surface of the reflective electrode so that the surface facing to the liquid crystal layer (the surface on which an alignment film is formed) is planarized.
In another embodiment of the second liquid crystal device in accordance with the present invention, the reflective electrode is a composite of a reflective layer and a transparent electrode layer.
According to this embodiment, the reflective layer reflects external light, and the transparent electrode layer applies a driving voltage to the liquid crystal even if the reflective electrode is not composed of a reflective and conductive single film.
The above-mentioned object of the present invention is also achieved by a second electronic apparatus provided with the second liquid crystal device.
The second electronic apparatus in accordance with the present invention uses a transflective liquid crystal device or a color transflective liquid crystal device without double imaging and blurred imaging due to parallax, and can change a display mode between a reflective mode and a transmissive mode. Thus, the electronic apparatus can display high-quality images in any lighted or dark environment regardless of the level of ambient or external light.
The object of the present invention is also achieved by a third liquid crystal device including a pair of first and second transparent substrates; a liquid crystal layer disposed between the first and second substrates; a plurality of reflective electrodes with a predetermined gap formed on a face of the second substrate on the side of the liquid crystal layer; a transparent electrode formed on a face of the first substrate on the side of the liquid crystal layer, and opposing to the reflective electrodes and gaps between the reflective electrodes; and an illumination unit provided on an another face of the second substrate on the opposite side of the liquid crystal layer.
According to the third liquid crystal device of the present invention, the reflective electrode reflects external light incident on the first substrate towards the liquid crystal layer in a reflective display mode. Since the reflective electrode is provided on the face of the second substrate on the side of the liquid crystal layer, no gap is substantially formed between the liquid crystal layer and the reflective electrode. Thus, double imaging and blurred imaging due to parallax do not occur. On the other hand, light which is incident on the second substrate passes through a gap between the reflective electrodes and is incident on the liquid crystal layer in a transmissive display mode. Herein, an oblique electric field generated between a portion of the transparent electrode facing the gap between the reflective electrodes, and the reflective electrode can drive the liquid crystal. Thus, light from the light source which passes through the gap between the reflective electrodes is driven by the oblique electric field to facilitate bright display. Whitening by non-driven liquid crystal portions facing the gap between the reflective electrodes can be simultaneously prevented, and thus display defects due to the gap between the reflective electrodes can be reduced. Since covering the gap between the reflective electrodes with a shading film (called a xe2x80x9cblack matrixxe2x80x9d or a xe2x80x9cblack maskxe2x80x9d) is not necessary, this structure has advantages in production and design of the device.
The third liquid crystal device can be driven by various conventional driving system, such as a passive matrix driving system, a TFT active matrix driving system, a TFD active matrix driving system, or a segment driving system. Thus, the reflective electrodes may be composed of a plurality of stripe electrodes or a plurality of rectangular electrodes depending on the applied driving system.
The width of the gap between the reflective electrodes is in a range of preferably 0.01 xcexcm to 20 xcexcm, and is more preferably 1 xcexcm to 5 xcexcm. A reflective display mode and a transmissive display mode can be simultaneously achieved without deterioration of image quality due to provision of the gap, since a viewer cannot recognize such a structure. Preferably, the gap has an area ratio of 5% to 30% with respect to the reflective electrode. Such a ratio can moderate decreased brightness in a reflective display mode, and achieves a transmissive display mode by light incident on the liquid crystal layer via the gap between the reflective electrodes. In the transmissive display mode, bright high-quality display by the liquid crystal at the gap portion is achieved by increasing luminance of the light source in the illumination unit, even if only a small portion of the overall liquid crystal is driven by the oblique electric field.
In an embodiment of the third liquid crystal in accordance with the present invention, a plurality of long reflective electrodes is formed, and an angle xcfx86 between the alignment direction of liquid crystal molecules, which lie substantially in the center between the transparent electrode and the reflective electrodes, and the longitudinal direction of the reflective electrodes is in a range of xe2x88x9260xc2x0xe2x89xa6xcfx86xe2x89xa660xc2x0.
According to this embodiment, long reflective electrodes, such as stripe- or rectangular-reflective electrodes, are formed, and the angle between the alignment direction of liquid crystal molecules, which lie substantially in the center between the transparent electrode and the reflective electrode and have the highest mobility, and the longitudinal direction of the reflective electrode shifts by 30xc2x0 or more from a right angle. When a voltage is applied between the transparent electrode and the reflective electrode, the alignment state of the liquid crystal molecules changes satisfactorily without formation of a tilt domain. Thus, the threshold voltage during driving of the liquid crystal can be reduced, resulting in reduced power consumption of the liquid crystal device. Furthermore, display defects, such as disclination, due to the tilt domain in the liquid crystal layer, are avoidable. A significant tilt domain is generated if the angle xcfx86 is outside the range of xe2x88x9260xc2x0xe2x89xa6xcfx86xe2x89xa660xc2x0, because the alignment direction of the liquid crystal molecules is perpendicular to the longitudinal direction of the reflective electrode. Thus, the driving voltage increases. The above advantage is particularly noticeable in a range of xe2x88x9230xc2x0xe2x89xa6xcfx86xe2x89xa630xc2x0.
In another embodiment of the third liquid crystal device of the present invention, an angle "psgr" between the alignment direction of a liquid crystal molecule in the vicinity of the reflective electrode and the longitudinal direction of the reflective electrode is in a range of xe2x88x9230xc2x0xe2x89xa6"psgr"xe2x89xa630xc2x0.
According to this embodiment, the alignment direction of the liquid crystal molecule in the vicinity of the reflective electrode having a predetermined pretilt angle is nearly parallel to, rather than perpendicular to, the longitudinal direction of the reflective electrode. Thus, there is substantially no possibility of the liquid crystal molecule at the substrate interface being reverse-tilted by the effect of the oblique electric field. Display defects such as disclination due to the reverse tilt domain are, therefore, avoidable. Thus, the threshold voltage during driving of the liquid crystal can be reduced, resulting in reduced power consumption of the liquid crystal device. If the angle "psgr" is in a range outside xe2x88x9230xc2x0xe2x89xa6"psgr"xe2x89xa630xc2x0, the liquid crystal molecule at the substrate interface is noticeably reverse-titled by the effect of the oblique electric field to cause display defects. Furthermore, the driving voltage increases, resulting in increased power consumption. The above advantage is particularly noticeable in a range of xe2x88x9210xc2x0xe2x89xa6"psgr"xe2x89xa610xc2x0.
In another embodiment of the third liquid crystal device in accordance with the present invention, the device further includes a first polarizer provided on another face of the first substrate on the opposite side of the liquid crystal layer, and at least one first retardation film disposed between the first substrate and the first polarizer.
According to this embodiment, the first polarizer primarily achieves satisfactory display control in both the reflective and transmissive display modes, and the first retardation film primarily reduces effects on tonality, such as coloring, due to the wavelength dispersion of light.
In another embodiment of the third liquid crystal device in accordance with the present invention, the device further includes a second polarizer disposed between the second substrate and the illumination unit, and at least a second retardation film disposed between the second substrate and the second polarizer.
According to this embodiment, the second polarizer primarily achieves satisfactory display control in the transmissive display mode, and the second retardation film primarily reduces effects on tonality, such as coloring, due to the wavelength dispersion of light.
In another embodiment of the third liquid crystal device in accordance with the present invention, the reflective electrode contains 95% by weight or more of aluminum and has a thickness of 10 nm to 40 nm.
According to this embodiment, a thin transflective type reflective electrode is formed. According to experiments, the transflective type reflective electrode has a transmittance of 1% to 40% and a reflectance 50% to 95% within the above thickness range.
In another embodiment of the third liquid crystal device in accordance with the present invention, the device further includes a color filter provided between the reflective electrode and the first substrate.
According to this embodiment, reflective color display by external light and transmissive color display using an illumination unit are available. Preferably, the color filter has a transmittance of 25% or more for light of any wavelength within a range of 380 nm to 780 nm. Bright reflective and transmissive color displays are thereby achieved.
In another embodiment of the third liquid crystal device in accordance with the present invention, the device further includes a diffuser on another face of the first substrate on the opposite side of the liquid crystal layer.
According to this embodiment, the diffuser makes the mirror face of the reflective electrode look as a diffusing face (white surface). Diffusion by the diffuser enables display from a wide view angle. The diffuser may be disposed at any position above the face of the first substrate on the opposite side of the liquid crystal layer. Preferably, the diffuser is disposed between the polarizer and the first substrate in consideration of the effect of back scattering (scattering of external light towards the incident side of it). The back scattering not contributing to the display of the liquid crystal device causes a decreased contrast in a reflective display mode. When the diffuser is disposed between the polarizer and the first substrate, the polarizer can reduce the quantity of light of back scattering to approximately one-half.
In another embodiment of the third liquid crystal device in accordance with the present invention, the reflective electrode has irregularities.
According to this embodiment, the irregularities eliminate the mirroring on the face of the reflective electrode and render the mirror face into a diffusing face (white face). Diffusion by the irregularities enables display with a wide view angle. The irregularities may be formed by forming a photosensitive acrylic resin layer under the reflective electrode, or by roughening the underlying glass substrate with aqueous hydrogen fluoride. It is preferable in order to achieve satisfactory alignment of the liquid crystals that a transparent planarization film be formed on the irregular surface of the reflective electrode so that the surface facing the liquid crystal layer (the surface on which an alignment film is formed) is planarized.
In another embodiment of the third liquid crystal device in accordance with the present invention, the reflective electrode is a composite of a reflective layer and a transparent electrode layer.
According to this embodiment, the reflective layer of the transflective electrode reflects external light, and the transparent electrode layer applies a driving voltage to the liquid crystal even if the reflective electrode is not composed of a reflective and conductive single film.
The above-mentioned object of the present invention is also achieved by a third electronic apparatus provided with the third liquid crystal device.
The third electronic apparatus in accordance with the present invention uses a transflective liquid crystal device or a color transflective liquid crystal device without double imaging and blurred imaging due to parallax, and can change a display mode between a reflective mode and a transmissive mode. Thus, the electronic apparatus can display high-quality images in any lighted or dark environment regardless of the level of ambient or external light.
The object of the present invention is also achieved by a fourth liquid crystal device including (i) a transflective liquid crystal panel comprising a pair of first and second transparent substrates; a liquid crystal layer disposed between the first and second substrates; a transparent electrode formed on a face of the first substrate facing the liquid crystal layer; a reflective electrode formed on a face of the second substrate facing the liquid crystal layer; and an illumination unit provided on an another face of the second substrate on the opposite side of the liquid crystal layer; and (ii) a driving means for driving the transparent electrode and the reflective electrode; wherein the liquid crystal panel is in a dim or black state when not driven.
According to the fourth liquid crystal device of the present invention, the reflective electrode reflects external light incident on the first substrate towards the liquid crystal layer in a reflective display mode. Since the reflective electrode is provided on the face of the second substrate facing the liquid crystal layer, no gap is substantially formed between the liquid crystal layer and the reflective electrode. Thus, double imaging and blurred imaging due to parallax do not occur. On the other hand, the reflective electrode comprising a transflective layer transmits light which emerges from the illumination unit and is incident on the second substrate towards the liquid crystal layer in a transmissive display mode. Thus, light from the light source achieves bright display in a dark environment. The transflective layer may be a reflective film having oblong slits or square fine openings so that light partly passes through the film, as in the above-mentioned first liquid crystal of the present invention, a thin metal transflective film having fine defects, such as pinhole defects or dimples, or a film which shows overall transflective characteristics. Alternatively, the layer may be composed of a plurality of stripes or island reflective electrodes formed with a predetermined gap. In the fourth liquid crystal device, the-liquid crystal panel driven between the transparent electrode and the reflective electrode by a driving means is a dim state when not driven. That is, it is driven by a normally black mode. Thus, optical leakage from boundaries between non-driven liquid crystal pixels or dots can be reduced in a transmissive display mode, resulting in transmissive display having a high contrast. Furthermore, undesirable reflection at boundaries between pixels or dots can be reduced in a reflective display mode, resulting in a display having a high contrast. Accordingly, an improved contrast is achieved in both a transmissive display mode and a reflective display mode without covering the gap between the reflective electrodes with a shading film (called a xe2x80x9cblack matrixxe2x80x9d or a xe2x80x9cblack maskxe2x80x9d). Since no shading film is provided, brightness does not decrease in a reflective display mode.
The fourth liquid crystal device can be driven by various conventional driving system, such as a passive matrix driving system, a TFT active matrix driving system, a TFD active matrix driving system, or a segment driving system.
In another embodiment of the fourth liquid crystal device in accordance with the present invention, the device further includes a first polarizer provided on another face of the first substrate on the opposite side of the liquid crystal layer, and at least one first retardation film disposed between the first substrate and the first polarizer.
According to this embodiment, the first polarizer primarily achieves satisfactory display control in both the reflective and transmissive display modes, and the first retardation film primarily reduces effects on tonality, such as coloring, due to the wavelength dispersion of light.
In another embodiment of the fourth liquid crystal device in accordance with the present invention, the device further includes a second polarizer disposed between the second substrate and the illumination unit, and at least a second retardation film disposed between the second substrate and the second polarizer.
According to this embodiment, the second polarizer primarily achieves satisfactory display control in the transmissive display mode, and the second retardation film primarily reduces effects on tonality, such as coloring, due to the wavelength dispersion of light.
In another embodiment of the fourth liquid crystal device in accordance with the present invention, the reflective electrode contains 95% by weight or more of aluminum and has a thickness of 10 nm to 40 nm.
According to this embodiment, a thin transflective type reflective electrode is formed. According to experiments, the transflective type reflective electrode has a transmittance of 1% to 40% and a reflectance 50% to 95% within the above thickness range.
In another embodiment of the fourth liquid crystal device in accordance with the present invention, the device further includes a color filter provided between the reflective electrode and the first substrate.
According to this embodiment, reflective color display by external light and transmissive color display using an illumination unit are available. Preferably, the color filter has a transmittance of 25% or more for light of any wavelength within a range of 380 nm to 780 nm. Bright reflective and transmissive color display is thereby achieved.
In another embodiment of the fourth liquid crystal device in accordance with the present invention, the device further includes a diffuser on another face of the first substrate on the opposite side of the liquid crystal layer.
According to this embodiment, the diffuser makes the mirror face of the reflective electrode a diffusing face (white surface). Diffusion by the diffuser enables display with a wide view angle. The diffuser may be disposed at any position above the face of the first substrate on the opposite side of the liquid crystal layer. Preferably, the diffuser is disposed between the polarizer and the first substrate in consideration of the effect of back scattering (scattering of external light towards the incident side of it). The back scattering not contributing to the display of the liquid crystal device causes a decreased contrast in a reflective display mode. When it is disposed between the polarizer and the first substrate, the polarizer can reduce the quantity of light of back scattering to approximately one-half.
In another embodiment of the fourth liquid crystal device in accordance with the present invention, the reflective electrode has irregularities.
According to this embodiment, the irregularities eliminate the mirroring on the face of the reflective electrode and render the mirror face into a diffusing face (white face). Diffusion by the irregularities enables display with a wide view angle. The irregularities may be formed by forming a photosensitive acrylic resin layer under the reflective electrode, or by roughening the underlying glass substrate with aqueous hydrogen fluoride. It is preferable in order to achieve satisfactory alignment of the liquid crystals that a transparent planarization film be formed on the irregular surface of the reflective electrode so that the surface facing to the liquid crystal layer (the surface on which an alignment film is formed) is planarized.
In another embodiment of the fourth liquid crystal device in accordance with the present invention, the reflective electrode is a composite of a reflective layer and a transparent electrode layer.
According to this embodiment, the reflective layer of the transflective electrode reflects external light, and the transparent electrode layer applies a driving voltage to the liquid crystal even if the reflective electrode is not composed of a reflective and conductive single film.
The above-mentioned object of the present invention is also achieved by a fourth electronic apparatus provided with the fourth liquid crystal device.
The fourth electronic apparatus in accordance with the present invention uses a transflective liquid crystal device or a color transflective liquid crystal device without double imaging and blurred imaging due to parallax, and can change a display mode between a reflective mode and a transmissive mode. Thus, the electronic apparatus can display high-quality images in any lighted or dark environment regardless of the level of ambient or external light.